Techno-economic analysis of cyanobacterial PHB bioplastic production

Abstract

Poly(3-hydroxybutyrate) (PHB) is a promising bioplastic compound which is produced by certain prokaryotic microbes such as some species of photosynthetic cyanobacteria. The production of cyanobacterial PHB has the potential to reduce traditional PHB production costs through using atmospheric CO2 as a carbon substrate, as opposed to using expensive organic carbon substrates needed for heterotrophic PHB production. This techno-economic analysis explores the financial profitability of using open raceway ponds to cultivate the cyanobacteria and solvent extraction on biomass to produce 10,000 tonnes of PHB per year. With a 10% PHB yield (10% PHB mass fraction of cell dry weight) used, the capital cost for the plant was $193.5 M USD and the operating cost was $147.3 M USD per year. At $4000 per tonne for PHB, the revenue of this plant was only $40 M USD per year, resulting in a 20-year Net Present Value (NPV) of -$1.8B USD. The breakeven minimum PHB selling price (for a zero 20-year NPV) was $18,339 USD per tonne. From the sensitivity analysis it was revealed that the key driver behind profitability of cyanobacterial PHB production is PHB yield. Lastly, seven different hypothetical scenarios are explored to increase the economic viability of the cyanobacterial production. These strategies ranged from additional revenue streams from pigment extraction, treatment of wastewater, to decreasing capital costs by using deep ‘PHB ripening ponds’. Operational costs were reduced through use of flocculants, solar power purchase agreements and an on-site anaerobic digester to reduce both energy and nutrient costs through digestate use as pond media. The optimistic combination of all these factors resulted in a final minimum PHB selling price of $7704 USD per tonne; still roughly twice the current market value of PHB.